Boiler

ABSTRACT

Provided is a boiler including: a plurality of heat transfer tubes arranged to form a cylindrical shape between an upper header and a lower header to constitute a heat transfer tube row; and a plurality of longitudinal fins provided to close gaps between the heat transfer tubes without connecting the adjacent heat transfer tubes, the plurality of longitudinal fins being provided to a portion other than one of one end in a vertical direction of the heat transfer tube row and a part in a peripheral direction thereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to various boilers including a steam boiler, a hot water boiler, a heat medium boiler, a waste heat boiler, and an exhaust gas boiler. In particular, the present invention relates to a multitubular boiler including a boiler body and longitudinal fins, the boiler body having a plurality of vertical heat transfer tubes arranged to form a cylindrical shape so as to connect an upper header to a lower header, the longitudinal fins being provided, in at least a part in a peripheral direction of the plurality of the vertical heat transfer tubes arranged to form the cylindrical shape, to gaps between the adjacent vertical heat transfer tubes.

The subject application claims a benefit of the priority of Japanese Patent Application No. 2007-112228 filed on Apr. 20, 2007, and contents thereof are herein incorporated.

2. Description of the Related Art

There are known as multitubular boilers ones disclosed in Japanese Patent Application Laid-open No. Sho 62-155401 (page 3, line 19 of upper left column to line 14 of lower left column, FIGS. 1 to 3) and Japanese Patent Application Laid-open No. 2004-225944. The boiler body of the boiler of this type includes the plurality of the water tubes between the upper header and the lower header each formed in an annular shape. The plurality of the water tubes are arranged in the peripheral direction of the upper header and the lower header in a form of inner and outer concentric circles. The plurality of the water tubes constituting the inner water tube row is called inner water tubes. The plurality of the water tubes constituting the outer water tube row is called outer water tubes. The inner water tubes are provided with the inner longitudinal fins downwardly extending from the upper header. The outer water tubes are provided with the outer longitudinal fins upwardly extending from the lower header.

In the boiler including the above-mentioned boiler body, the inside of the inner water tube row is the combustion chamber, and the space between the inner water tube row and the outer water tube row is the combustion gas flow path. At the lower portion of the inner water tube row, the combustion chamber communicates with the combustion gas flow path through the gaps between the inner water tubes formed in the portion where the inner longitudinal fins are not provided. Further, at the upper portion of the outer water tube row, the combustion gas flow path communicates with the flue through gaps between the outer water tubes formed in the portion where the outer longitudinal fins are not provided.

When a fuel is burned so as to generate flame from a burner installed in an upper portion of the boiler body toward the combustion chamber, a combustion gas is reversed in a lower portion of the combustion chamber and flows upwardly through the combustion gas flow path between the inner water tube row and the outer water tube row to be discharged as an exhaust gas to the flue from the upper portion of the boiler body. In the meantime, the combustion gas undergoes heat exchange with water in each of the water tubes, thereby allowing the water in each of the water tubes to be heated.

In the conventional boiler body, as clearly described in Japanese Patent Application Laid-open No. Sho 62-155401, both ends in the width direction of the inner longitudinal fin are welded to the outer peripheral surface of the adjacent inner water tubes. That is, the adjacent inner water tubes are connected to each other through an intermediation of the inner longitudinal fin.

In the case where the adjacent inner water tubes are connected to each other through the intermediation of the inner longitudinal fin as disclosed in Japanese Patent Application Laid-open No. Sho 62-155401, both sides of the longitudinal fin are restricted. Accordingly, thermal expansion of the inner water tubes or the longitudinal fins due to combustion in the combustion chamber cannot be relieved. In particular, the inner water tubes are subjected to high thermal stress because combustion gas temperature is high.

In order to relax the thermal stress, in the invention disclosed in Japanese Patent Application Laid-open No. 2004-225944, the height positions of the lower ends of the adjacent inner longitudinal fins are made different. However, also in this case, both ends in the width direction of the inner longitudinal fin are also welded to the outer surfaces of the adjacent inner water tubes. Accordingly, fundamental solution for relaxing the thermal stress is not reached. Further, the inner longitudinal fins have different sizes, so commonality of components cannot be achieved.

Further, in either conventional technologies, both ends in the width direction of the inner longitudinal fin are welded to the outer peripheral surfaces of the adjacent inner water tubes, so the number of welding processes tends to increase. Moreover, regarding either of the inner water tube row and the outer water tube row, in order to weld both ends of the longitudinal fin to the outer peripheral surfaces of the water tubes, it is necessary that the inner water tubes and the outer water tubes be first installed between the upper header and the lower header, and the longitudinal fins are then welded to the inner water tubes and the outer water tubes. Accordingly, the longitudinal fins of the inner water tubes constituting the inner water tube row cannot be welded from an outer side of a furnace, and the longitudinal fins of the outer water tubes constituting the outer water tube row cannot be welded from an inner side of the furnace. As a result, the water tubes and the longitudinal fins are not firmly integrated to each other, so there is room for improvement in heat conductivity from the longitudinal fins to the water tubes and mounting strength.

SUMMARY OF THE INVENTION

An object of the present invention is to relax thermal stress acting on water tubes or longitudinal fins and to achieve commonality of components of inner longitudinal fins, improvement in assembling workability of a boiler body, improvement in heat conductivity from longitudinal fins to the water tubes, and improvement in mounting strength of the longitudinal fins with respect to the water tubes.

According to a first aspect of the present invention, there is provided a boiler including: a plurality of heat transfer tubes arranged to form a cylindrical shape between an upper header and a lower header to constitute a heat transfer tube row; and a plurality of longitudinal fins provided to close gaps between the heat transfer tubes without connecting the adjacent heat transfer tubes, the plurality of longitudinal fins being provided to a portion other than one of one end in a vertical direction of the heat transfer tube row and a part in a peripheral direction thereof.

In the boiler according to the first aspect of the present invention, the adjacent heat transfer tubes are not connected to each other by the longitudinal fins, so thermal stress caused in the heat transfer tubes and the longitudinal fins can be relaxed. Further, the gaps between the adjacent heat transfer tubes are closed by the longitudinal fins, so short path of the combustion gas can be prevented.

In the boiler according to the first aspect of the present invention: the heat transfer tube row may include, in order to close gaps between each of the plurality of heat transfer tubes and the heat transfer tubes adjacent to both sides thereof, a plurality of double-fin heat transfer tubes each having the longitudinal fins on both sides thereof and a plurality of no-fin heat transfer tubes free from having the longitudinal fin; the plurality of double-fin heat transfer tubes and the plurality of no-fin heat transfer tubes may be alternately arranged one by one; and the boiler may further include a combustion chamber on an inner side of the heat transfer tube row, which communicates with a combustion gas flow path on an outer side of the heat transfer tube row through a portion free from having the longitudinal fin at the one end in the vertical direction of the heat transfer tube row.

In the boiler according to the first aspect of the present invention, the heat transfer tube row is formed of alternately arranging the double-fin heat transfer tubes and the single-fin heat transfer tubes one by one. Accordingly, commonality of components can be achieved and assembling workability can be improved. Further, after the longitudinal fins are fixed to the heat transfer tubes, those may be arranged between the upper header and the lower header, so operability at the time of assembly is improved. Further, the longitudinal fins can be welded to the heat transfer tubes in advance not only on an outer side of a furnace but also on an inner side of the furnace. Accordingly, mounting strength of the longitudinal fins with respect to the heat transfer tubes is improved, and further, owing to firm integration between the heat transfer tubes and the longitudinal fins, heat conductivity from the longitudinal fins to the heat transfer tubes can be improved.

In the boiler according to the first aspect of the present invention: the heat transfer tube row may include, in order to close gaps between each of the plurality of heat transfer tubes and the heat transfer tube adjacent to one side thereof, a plurality of single-fin heat transfer tubes each having the longitudinal fin on one side thereof; and the boiler may further include a combustion chamber on an inner side of the heat transfer tube row, which communicates with a combustion gas flow path on an outer side of the heat transfer tube row through a portion free from having the longitudinal fin at the one end in the vertical direction of the heat transfer tube row.

In the boiler according to the first aspect of the present invention, the heat transfer tube row is formed by successively arranging the single-fin water tubes, so the commonality of the components can be achieved and the assembling workability can be improved. Further, after the longitudinal fins are fixed to the heat transfer tubes, those may be arranged between the upper header and the lower header, so operability at the time of assembly is improved. Further, the longitudinal fins can be welded to the heat transfer tubes in advance not only on an outer side of a furnace but also on an inner side of the furnace. Accordingly, mounting strength of the longitudinal fins with respect to the heat transfer tubes is improved, and further, owing to firm integration between the heat transfer tubes and the longitudinal fins, heat conductivity from the longitudinal fins to the heat transfer tubes can be improved.

In the boiler according to the first aspect of the present invention, the plurality of longitudinal fins may have a size achieving closure of gaps between the adjacent plurality of heat transfer tubes owing to thermal expansion by one of a combustion gas and an exhaust gas.

In the boiler according to the first aspect of the present invention, since the longitudinal fins close the gaps between the adjacent heat transfer tubes owing to the thermal expansion, the short path of the combustion gas can be prevented more reliably.

According to a second aspect of the present invention, there is provided a boiler including: a plurality of heat transfer tubes arranged adjacent to each other; and a longitudinal fin provided between the adjacent heat transfer tubes, in which: one end of the longitudinal fin is fixed to one of the adjacent heat transfer tubes; and another end of the longitudinal fin abuts on another of the adjacent heat transfer tubes owing to thermal expansion by combustion of a fuel in a combustion chamber.

In the boiler according to the second aspect of the present invention, since the adjacent heat transfer tubes are not connected by each of the longitudinal fins, thermal stress caused in the heat transfer tubes and the longitudinal fins can be relaxed. Further, in a portion where the longitudinal fin is provided, gaps between the adjacent heat transfer tubes are reliably closed owing to the thermal expansion of the longitudinal fin.

In the boiler of the present invention, the thermal stress acting on the longitudinal fins or the heat transfer tubes can be relaxed. Further, it is possible to achieve commonality of components of the inner longitudinal fins, improvement in assembling workability of the boiler body, improvement in the heat conductivity from the longitudinal fins to the water tubes, and improvement in the mounting strength of the longitudinal fins with respect to the water tubes.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a schematic vertical sectional view showing a boiler according to Embodiment 1 of the present invention;

FIG. 2 is a sectional view taken along the line II-II of FIG. 1;

FIG. 3 is an enlarged cross sectional view schematically showing a part of an inner water tube row of the boiler shown in FIG. 1 and showing a cold state of the boiler;

FIG. 4 is an enlarged cross sectional view schematically showing the part of the inner water tube row of the boiler shown in FIG. 1 and showing a combustion state of the boiler;

FIG. 5 is an enlarged cross sectional view schematically showing a part of the inner water tube row of the boiler shown in FIG. 1 and showing a state where an inner longitudinal fin of a double-fin water tube is disposed on a straight line connecting centers of adjacent inner water tubes;

FIG. 6 is an enlarged cross sectional view schematically showing a part of an outer water tube row of the boiler shown in FIG. 1;

FIG. 7 is a schematic cross sectional view showing a modification of the inner water tube row of the boiler shown in FIG. 1;

FIG. 8 is a schematic cross sectional view showing a boiler according to Embodiment 2 of the present invention; and

FIG. 9 is a schematic cross sectional view showing a boiler according to Embodiment 3 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, embodiment modes of the present invention will be described.

A boiler according to the present invention is not limited to a certain type and is, for example, a steam boiler, a hot water boiler, a heat medium boiler, a waste heat boiler, or an exhaust gas boiler. In any case, the boiler is a multitubular boiler and is typically a multitubular small once-through boiler.

Specifically, the boiler includes an upper header, a lower header, and a boiler body including a plurality of heat transfer tubes connecting the upper header to the lower header. The upper header and the lower header are arranged at a vertical distance in parallel to each other. Each of the upper header and the lower header forms a hollow annular shape. All the plurality of the heat transfer tubes are vertically arranged and are disposed between the upper header and the lower header. That is, upper ends of the heat transfer tubes are connected to the upper header and lower ends thereof are connected to the lower header. The heat transfer tubes are arranged between the upper header and the lower header in a peripheral direction thereof, thereby constituting a heat transfer tube row of a cylindrical shape.

The heat transfer tube row is not limited to a single row, and may be two rows, three rows, or more. For example, the boiler body includes an inner heat transfer tube row and an outer heat transfer tube row. In this case, the inner heat transfer tube row includes a plurality of inner heat transfer tubes arranged to form a cylindrical shape between the upper header and the lower header. Further, the outer heat transfer tube row includes a plurality of outer heat transfer tubes arranged to form a cylindrical shape between the upper header and the lower header so as to surround the inner heat transfer tube row. In the above-mentioned case where there are provided the plurality of the heat transfer tube rows, the heat transfer tube rows are arranged in concentric cylindrical shapes.

The boiler body is normally closed at one end thereof in a vertical direction and has a burner at the other end thereof in the vertical direction. With this structure, an inside of the heat transfer tube row arranged on an innermost side constitutes a combustion chamber. It is possible to burn a fuel so that flame is generated from the burner toward the combustion chamber. Note that, in a case of the waste heat boiler or the exhaust gas boiler, the boiler body is closed at one end thereof in the vertical direction and has an opening portion at the other end thereof in the vertical direction, through which an exhaust gas is introduced into the boiler. That is, in the case of the waste heat boiler or the exhaust gas boiler, an exhaust gas is introduced into a space on an inner side of the heat transfer tube row arranged on the innermost side. In both cases, an outer peripheral portion of the boiler body is covered by a boiler body cover.

The boiler body cover is a cylindrical member provided between the upper header and the lower header so as to surround the heat transfer tube rows. An upper end of the boiler body cover and the upper header are hermetically sealed. A lower end of the boiler body cover and the lower header are also hermetically sealed. The boiler body cover is connected to a flue. A combustion gas from the combustion chamber (exhaust gas in the case of waste heat boiler or exhaust gas boiler) undergoes heat exchange with a heat carrier (such as water) flowing through each of the heat transfer tubes, and is then discharged from the flue as the exhaust gas.

In order to achieve effective heat exchange with a heat carrier flowing through the heat transfer tubes, the combustion gas flows through a space between the outer heat transfer tube row and the inner heat transfer tube row and a space between the outer heat transfer tube row and the boiler body cover through a predetermined passage. Alternatively, the combustion gas flows through one of the space between the outer heat transfer tube row and the inner heat transfer tube row, and the space between the heat transfer tube rows and the boiler body cover through the predetermined passage. In order to define the passage, a part or an entire portion of the inner heat transfer tube row is provided with, except at an end in the vertical direction thereof or a part in the peripheral direction thereof, inner longitudinal fins provided to close gaps between the adjacent inner heat transfer tubes. Further, a part or an entire portion of the outer heat transfer tube row is provided with, except at an end in the vertical direction thereof or a part in the peripheral direction thereof, outer longitudinal fins provided to close gaps between the adjacent outer heat transfer tubes.

In this case, the longitudinal fins in the part or the entire portion of each of the heat transfer tube rows are provided without connecting the adjacent heat transfer tubes. As structures therefor, the following three embodiment modes can be suggested.

In a first embodiment mode of the present invention, each of the heat transfer tube rows is formed of a plurality of double-fin heat transfer tubes and a plurality of no-fin heat transfer tubes which are alternately arranged one by one. The double-fin heat transfer tube is a heat transfer tube having longitudinal fins on both sides thereof so that gaps between each of the heat transfer tubes and the heat transfer tubes adjacent to both sides thereof are closed. The no-fin heat transfer tube is a heat transfer tube which does not have the longitudinal fin. Each of the double-fin heat transfer tubes is provided such that distal ends of the longitudinal fins thereof are close to outer peripheral surfaces of the other adjacent heat transfer tubes. In this embodiment, in a case where the longitudinal fins are provided over an entire periphery of the heat transfer tube row, in consideration to a structure where the plurality of the double-fin heat transfer tubes and the plurality of the no-fin heat transfer tubes are alternately provided, it is preferable that the heat transfer tube row be formed of an even number of heat transfer tubes. Note that when single-fin heat transfer tubes described below are used in a part of the heat transfer tube row, the heat transfer tube row can be formed of an odd number of heat transfer tubes.

In a second embodiment mode of the present invention, the heat transfer tube row is formed of a plurality of single-fin heat transfer tubes. The single-fin heat transfer tubes are heat transfer tubes each having a longitudinal fin on one side thereof such that gaps between each of the heat transfer tubes and the heat transfer tube adjacent to one side thereof are closed. Each of the single-fin heat transfer tubes is provided such that a distal end of the longitudinal fin is close to an outer peripheral surface of another adjacent heat transfer tube.

In a third embodiment of the present invention, the heat transfer tube row is formed of a plurality of double-fin heat transfer tubes. In this case, the double-fin heat transfer tubes are provided such that distal ends of the longitudinal fins are close to distal ends of the longitudinal fins of the other adjacent heat transfer tubes. That is, the adjacent double-fin heat transfer tubes are arranged such that distal ends of the longitudinal fins thereof abut each other.

In all the embodiment modes, it is preferable that the longitudinal fins have such a size that achieves tight closure of gaps between the adjacent heat transfer tubes through thermal expansion thereof owing to heating by the combustion gas. That is, each of the gaps formed between the distal end of the longitudinal fins and the adjacent heat transfer tube main body or the longitudinal fin thereof is preferably substantially the same as an amount of elongation involved in temperature rise of the longitudinal fin at the time of operation of the boiler. As a result, in the first embodiment mode of the present invention, each of the longitudinal fins of the double-fin heat transfer tube abuts on the outer peripheral surface of another adjacent heat transfer tube. Further, in the second embodiment of the present invention, the longitudinal fin of the single-fin heat transfer tube abuts on the outer peripheral surface of another adjacent heat transfer tube. Further, in the third embodiment of the present invention, each of the longitudinal fins of the double-fin heat transfer tube abuts on one of the longitudinal fins of another adjacent double-fin heat transfer tube.

In a case where the heat transfer tube row of those structures is applied to the inner heat transfer tube row, the combustion chamber on the inner side of the heat transfer tube row communicates with a combustion gas flow path on an outer side of the heat transfer tube row through a portion free from having the longitudinal fins at one end in the vertical direction of the heat transfer tube row or in a part in a peripheral direction thereof.

The double-fin heat transfer tube and the single-fin heat transfer tube may be formed by extrusion molding such that the longitudinal fin(s) and the heat transfer tube main body are integrated with each other. However, a normal heat transfer tube with a fin is formed by disposing a square bar constituting the longitudinal fin to an outer peripheral surface of a circular tube constituting the heat transfer tube main body in an axial direction of the circular tube, and welding the square bar to the circular tube. With the either heat transfer tubes, after the longitudinal fin(s) is provided to the heat transfer tube main body, the heat transfer tube can be provided between the upper header and the lower header. That is, when the heat transfer tubes are installed between the upper header and the lower header, the longitudinal fins can be welded to the heat transfer tubes in advance not only on an outer side of a furnace but also on an inner side of the furnace. As a result, the mounting strength is improved and the heat conductivity from the longitudinal fin(s) to the heat transfer tube is also improved because the longitudinal fin(s) is firmly integrated with the heat transfer tube.

Meanwhile, the longitudinal fin provided to the double-fin heat transfer tube or the single-fin heat transfer tube is typically provided so as to protrude radially outwardly from the heat transfer tube main body. In this case, when each of the longitudinal fins is arranged on a straight line connecting centers of the adjacent heat transfer tubes, the gaps between the adjacent heat transfer tubes can be closed at a minimum distance. Note that the longitudinal fins may be provided while being shifted to the inner side of the furnace or the outer side of the furnace. Further, the longitudinal fins may not necessarily protrude in the radius direction of the heat transfer tube main body.

Embodiment 1

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic vertical sectional view showing a boiler according to Embodiment 1 of the present invention. FIG. 2 is a sectional view taken along the line II-II of FIG. 1. A boiler 1 of this embodiment is a multitubular small once-through boiler including a boiler body 2 of a cylindrical shape. The boiler body 2 includes an upper header 3, a lower header 4, and a plurality of water tubes (heat transfer tubes) 5 and 6 arranged to form a cylindrical shape to connect the upper header 3 to the lower header 4.

The upper header 3 and the lower header 4 are arranged at a vertical distance in parallel to each other. Each of the upper header 3 and the lower header 4 forms a hollow annular shape. Further, the upper header 3 and the lower header 4 are arranged horizontally and coaxially.

The plurality of the water tubes 5 are vertically arranged. Upper ends of the water tubes 5 are connected to the upper header 3, and lower ends thereof are connected to the lower header 4. The water tubes 5 are successively arranged in a peripheral direction of the upper header 3 and the lower header 4, thereby constituting a water tube row forming a cylindrical shape. On the other hand, the plurality of the water tubes 6 are also vertically arranged, the upper ends of the water tubes 6 are connected to the upper header 3, and the lower ends of the water tubes 6 are connected to the lower header 4. The water tubes 6 are successively arranged in the peripheral direction of the upper header 3 and the lower header 4 on the outer side of the cylindrically arranged water tubes 5, thereby constituting the water tube row forming the cylindrical shape. In this embodiment, an inner water tube row 7 including the plurality of the water tubes 5 and an outer water tube row 8 including the plurality of the water tubes 6 are concentrically arranged. That is, the outer water tube row 8 is arranged so as to surround the inner water tube row 7. Note that, in the following, the water tubes 5 are referred to as inner water tubes and the water tubes 6 are referred to as outer water tubes.

The inner water tube row 7 is provided with, except for a predetermined region at a lower end thereof, inner longitudinal fins 9 such that gaps between the adjacent inner water tubes 5 are closed. That is, the gaps between the adjacent inner water tubes 5 are closed by the inner longitudinal fins 9 except for the predetermined region at the lower end thereof. In a portion of the inner water tube row 7, where the inner longitudinal fins 9 are not provided, the gaps between the adjacent inner water tubes 5 remain. The gaps constitute communication portions (hereinafter, referred to as inner row communication portions) 10 for establishing communication between spaces on the inner side and the outer side of the inner water tube row 7.

FIGS. 3 and 4 are enlarged cross sectional views each schematically showing a part of the inner water tube row 7. FIG. 3 shows a cold state of the boiler 1, and FIG. 4 shows a combustion state of the boiler 1. As shown in FIG. 3, the inner water tube row 7 is formed of a plurality of double-fin water tubes 11 and a plurality of no-fin water tubes 12 which are arranged alternately one by one. Each of the double-fin water tubes 11 is formed of the inner water tube 5 of a circular tube shape constituting the water tube main body and the two inner longitudinal fins 9 provided to both sides of the inner water tube 5 so as to radially protrude therefrom. On the other hand, each of the no-fin water tubes 12 is formed of the inner water tube 5 of the circular tube shape constituting the water tube main body and is not provided with the inner longitudinal fin 9.

The inner longitudinal fins 9 of the double-fin water tube 11 are provided so as to close the gaps between the double-fin water tube 11 and the two no-fin water tubes 12 adjacent to both sides thereof in the peripheral direction. Typically, the two inner longitudinal fins 9 of the double-fin water tube 11 are provided so as to protrude radially outwardly from the inner water tube 5. In this case, the inner longitudinal fins 9 may be provided so as to protrude in a diameter direction from both sides of the inner water tube 5, or may be provided on straight lines connecting the centers of the adjacent inner water tubes 5. Alternatively, the inner longitudinal fins 9 may be provided by being shifted to an inner side or an outer side of a furnace.

Each of the inner longitudinal fins 9 includes an elongated bar having a rectangular section and is arranged such that a longitudinal direction thereof is parallel to an axis of the inner water tube 5. A proximal end (one end in width direction) of the inner longitudinal fin 9 is welded (welding portion 13) onto the inner water tube 5 while being brought into abutment on the outer peripheral surface of the inner water tube 5. In this case, when the two inner longitudinal fins 9 are simultaneously welded to both sides of the inner water tube 5, warpage is less prone to occur in the inner water tube 5. Further, the proximal end of each of the inner longitudinal fins 9 is fillet-welded to the inner water tube 5 on the inner side and the outer side of the furnace over an entire longitudinal region. As a result, the inner water tube 5 and the inner longitudinal fins 9 are firmly integrated with each other. Accordingly, it is possible to improve mounting strength of the inner longitudinal fins 9 with respect to the inner water tube 5 and to improve heat conductivity from the inner longitudinal fins 9 to the inner water tube 5.

Each of the double-fin water tubes 11 is arranged such that the distal ends of the two inner longitudinal fins 9 welded to both sides are close to the outer peripheral surfaces of the adjacent no-fin water tubes 12. In this case, as occasion needs, the distal ends of the inner longitudinal fins 9 may be allowed to moderately abut on the outer peripheral surfaces of the no-fin water tubes 12 or a part of the distal ends may be allowed to abut thereon. In this case, a distance between each of the distal ends of the inner longitudinal fins 9 and the outer peripheral surface of the no-fin water tube 12 is set to an amount of elongation a involved in temperature rise of the inner longitudinal fins 9 at the time of combustion of the boiler 1 (see FIG. 5). For example, FIG. 5 shows a state where the inner longitudinal fin 9 of the double-fin water tube 11 is arranged on the straight line connecting the centers of the adjacent inner water tubes 5. In FIG. 5, when the gap between the adjacent inner water tubes 5 is δ and a width of the inner longitudinal fin 9 is L, the gap δ is equal to L+α. The width L of the inner longitudinal fin 9 is not particularly limited, but is preferably equal to or less than 10 mm for preventing burning, and is set to 6 mm, for example. Note that an outer diameter of the inner water tube 5 is normally about 50 mm.

In a case of this embodiment, to the inner water tube row 7, the inner longitudinal fins 9 are provided over the entire periphery thereof so as to close the gaps between the adjacent inner water tubes 5. As described above, the inner water tube row 7 includes the double-fin water tubes 11 and the no-fin water tubes 12 alternately arranged one by one. Accordingly, the inner water tube row 7 is preferably formed of the even number of inner water tubes 5. Note that, when single-fin water tubes 14 (see FIG. 7) described below are used in a part thereof, the inner water tube row 7 can be formed of the odd number of inner water tubes.

As described in this embodiment, when the double-fin water tubes 11 and the no-fin water tubes 12 are alternately arranged one by one, that is, when the adjacent inner water tubes 5 are not welded to each other, the double-fin water tubes 11 each having the two inner longitudinal fins 9 welded to both sides of the inner water tube 5 are manufactured in advance, and the double-fin water tubes 11 can be installed between the upper header 3 and the lower header 4. That is, in installing the heat-transfer tubes between the upper header 3 and the lower header 4, the longitudinal fins can be welded not only to the heat transfer tubes on the outer side of the furnace but also to the heat transfer tubes on the inner side of the furnace in advance. As a result, the mounting strength is improved, and further, the inner longitudinal fins 9 are firmly integrated with the inner water tubes 5, thereby making it possible to improve the heat conductivity from the inner longitudinal fins 9 to the inner water tubes 5.

The outer water tube row 8 is provided with, except for a predetermined region at the upper end thereof, outer longitudinal fins 15 such that gaps between the adjacent outer water tubes 6 are closed. That is, the gaps between the outer water tubes 6 are closed by the outer longitudinal fins 15 except for the predetermined region at the upper end thereof. In a portion of the outer water tube row 8, where the outer longitudinal fins 15 are not provided, gaps between the adjacent outer water tubes 6 remain. The gaps constitute communication portions (hereinafter, referred to as outer row communication portions) 16 for establishing communication between spaces on the inner side and the outer side of the outer water tube row 8.

FIG. 6 is an enlarged cross sectional view schematically showing a part of the outer water tube row 8. Similarly to the inner water tube row 7, the outer water tube row 8 of this embodiment is formed of the plurality of the double-fin water tubes 11 and the plurality of the no-fin water tubes 12 arranged alternately one by one. Each of the double-fin water tubes 11 is formed of the outer water tube 6 of the cylindrical shape constituting the water tube main body and the two outer longitudinal fins 15 provided to both sides of the outer water tube 6 so as to radially protrude therefrom. Each of the outer longitudinal fins 15 is welded to the outer water tube 6 in the same manner as that of the inner water tube row 7. However, a width of the outer longitudinal fin 15 may be larger than the width of the inner longitudinal fin 9. On the other hand, the no-fin water tube 12 is formed of the outer water tube 6 of the cylindrical shape constituting the water tube main body and is not provided with the outer longitudinal fin 15.

The outer water tube row 8 may also have a structure in which, similarly to the inner water tube row 7, owing to the thermal expansion by the combustion of the boiler 1, distal ends of the two outer longitudinal fins 15 of the double-fin water tubes 11 abut on the outer peripheral surfaces of the no-fin water tubes 12 adjacent to both sides thereof, respectively. Note that, in the case of the outer water tube row 8, in order to seal in a combustion gas or an exhaust gas by the outer water tube row 8, the distal end of each of the outer longitudinal fins 15 may be welded in advance after being abutted on the outer peripheral surface of the no-fin water tube 12.

In the outer water tube row 8, similarly to the inner water tube row 7, the double-fin water tubes 11 each having the two outer longitudinal fins 15 welded to both sides of the outer water tube 6 are manufactured in advance, and the double-fin water tubes 11 can be installed between the upper header 3 and the lower header 4. That is, when the heat transfer tubes are installed between the upper header 3 and the lower header 4, the longitudinal fins can be welded not only to the heat transfer tubes on the outer side of the furnace but also to the heat transfer tubes on the inner side of the furnace. As a result, the mounting strength is improved, and further the outer longitudinal fins 15 are firmly integrated with the outer water tubes 6, thereby making it possible to improve heat conductivity from the outer longitudinal fins 15 to the outer water tubes 6. As described above, in a case where, in order to seal in the combustion gas or the exhaust gas by the outer water tube row 8, the distal end of each of the outer longitudinal fins 15 is welded in advance to the outer peripheral surface of the no-fin water tube 12, it suffices that welding is performed from the outer side of the furnace (welding portion 18 is provided).

Meanwhile, according to needs, each of the inner water tubes 5 may be further provided with an inner lateral fin (not shown) protruding from the outer peripheral surface thereof. A plurality of inner lateral fins may be provided to each of the inner water tubes 5 at vertical intervals. Further, each of the inner lateral fins normally protrudes in a flange-like shape in a radially outward direction of each of the inner water tubes 5. Similarly, according to needs, each of the outer water tubes 6 may be further provided with an outer lateral fin (not shown) protruding from the outer peripheral surface thereof. A plurality of outer lateral fins may be provided to each of the outer water tubes 6 at vertical intervals. Further, each of the outer lateral fins normally protrudes in a flange-like shape in a radially outward direction of each of the outer water tubes 6. In this case, each of the lateral fins is inclined at a predetermined angle with respect to a horizontal direction, thereby making it possible to generate swirl flow of the combustion gas. Presence/absence of installation of the lateral fin, an installation region and an installation position thereof, the number of lateral fins to be installed, a shape and a size, and the like are appropriately set.

Further, between the upper header 3 and the lower header 4, a boiler body cover 17 of a cylindrical shape is provided so as to surround the outer water tube row 8. An upper end of the boiler cover 17 and the upper header 3 are hermetically sealed. A lower end of the boiler cover 17 and the lower header 4 are also hermetically sealed. To an upper portion of a peripheral wall of the boiler body cover 17, a flue 19 is connected. Note that the outer water tube row 8 may also serve as a part of the boiler body cover 17. In this case, the boiler body cover 17 is provided so as to connect a portion of the outer water tube row 8 having the outer longitudinal fins 15 to the upper header 3.

A lower surface of the upper header 3 is provided with a fireproof material 20 covering connection portions between the upper header 3 and the inner water tubes 5 and connection portions between the upper header 3 and the outer water tubes 6. An upper surface of the lower header 4 is also provided with another fireproof material 20 covering connection portions with respect to the inner water tubes 5 and connection portions between the lower header 4 and the outer water tubes 6. The fireproof material 20 on the lower header 4 side is provided so as to also close a central portion of the lower header 4. A central portion of the fireproof material 20 on the lower header 4 side has a recess of a columnar shape or a truncated cone shape formed therein.

Meanwhile, in the illustrated example, a lower end of each of the inner water tubes 5 is formed with a small diameter portion 21 having a diameter smaller than that of the other portion. The small diameter portions 21 are provided so as to ensure a predetermined flow rate of the combustion gas passing through the inner row communication portions 10. Accordingly, in a case where, even without the small diameter portions 21, the predetermined flow rate of the combustion gas passing through the inner row communication portions 10 can be ensured, the small diameter portions 21 are not necessary. A size of each of the inner row communication portions 10 depends on the gap between the adjacent inner water tubes 5 and a position of the lower end of the inner longitudinal fin 9 in a height direction thereof. Accordingly, instead of providing the small diameter portions 21, those dimensions may be adjusted. Note that, in the illustrated example, the small diameter portion 21 is not formed on the upper end of each of the outer water tubes 6. However, similarly to the inner water tubes 5, the small diameter portions 21 may be formed thereon.

In a central portion of the upper header 3, there is, provided a burner 22 for generating flame downwardly. The burner 22 is supplied with a fuel and a combustion air. By operating the burner 22, combustion of the fuel is performed in the boiler body 2. In this case, an inside of the inner water tube row 7 functions as a combustion chamber 23.

A combustion gas generated by the combustion of the fuel in the combustion chamber 23 is delivered to a combustion gas flow path 24 between the inner water tube row 7 and the outer water tube row 8 through the inner row communication portions 10. The combustion gas is discharged as an exhaust gas to the outside through the outer row communication portions 16 and the flue 19 of the boiler body cover 17. In the meantime, the combustion gas undergoes heat exchange with water in the inner water tubes 5 and water in the outer water tubes 6. As a result, the water in the water tubes is heated. The heated water can be taken out from the upper header 3 in a form of steam. The steam which is taken out is sent to steam using equipment (not shown) through a water separator (not shown) or the like.

In this embodiment, the inner water tube row 7 is provided with the inner longitudinal fins 9 provided to close the gaps between the adjacent inner water tubes 5. The outer water tube row 8 is provided with the outer longitudinal fins 15 provided to close the gaps between the adjacent outer water tubes 6. As a result, while flow of the combustion gas into the gaps between the inner water tubes 5 and into the gaps between the outer water tubes 6 is enabled, thereby preventing the gaps from being dead spaces. Further, by the inner longitudinal fins 9 and the outer longitudinal fins 15, heat conduction efficiency from the combustion gas to the inner water tubes 5 and the outer water tubes 6 can be enhanced. In addition, after the combustion gas is radially discharged from the entire periphery of the outer water tube row 8, the exhaust gas is introduced to the flue 19 through the space between the outer water tube row 8 and the boiler body cover 17. Accordingly, uniform flow of the exhaust gas over an entire area in the peripheral direction of the outer water tube row 8 can be realized.

FIG. 7 is a schematic cross sectional view showing a modification of the inner water tube row 7. As shown in FIG. 7, the inner water tube row 7 may be formed of a plurality of single-fin water tubes 14 which are successively arranged, instead of the plurality of the double-fin water tubes 11 and the plurality of the no-fin water tubes 12 which are alternately arranged one by one. Each of the single-fin water tubes 14 is formed of the inner water tube 5 of the cylindrical shape constituting the water tube main body, and the one inner longitudinal fin 9 provided to one side of the inner water tube 5 so as to protrude in the radius direction thereof. Each of the single-fin water tubes 14 is arranged such that the distal end of the one inner longitudinal fin 9 welded on the one side is close to the outer peripheral surface of the adjacent single-fin water tube 14. Also in this case, at the time of combustion of the boiler 1, the gaps between the inner water tubes 5 are completely closed owing to the thermal expansion of the inner longitudinal fins 9.

The inner water tube row 7 may be formed of the double-fin water tubes 11 which are successively arranged instead of the single-fin water tubes 14 which are successively arranged. In this case, each of the double-fin water tubes 11 is arranged such that the distal ends of the two inner longitudinal fins 9 welded to both sides abut on the distal ends of the inner longitudinal fins 9 of the double-fin water tubes 11 which are adjacent thereto. Also in this case, at the time of combustion of the boiler 1, the gaps between the inner water tubes 5 are completely closed owing to the thermal expansion of the inner longitudinal fins 9.

The modification as described above can be applied not only to the inner water tube row 7 but also to the outer water tube row 8 in the same manner. In a case where the outer water tube row 8 also serves as the boiler body cover 17, the distal ends of the outer longitudinal fins 15 are welded to the other adjacent outer water tubes 6 or the longitudinal fins 15 thereof in the same manner. Further, in the case of either modification, after the inner longitudinal fins 9 are welded to the inner water tubes 5 or the outer longitudinal fins 15 are welded to the outer water tubes 6, those are provided between the upper header 3 and the lower header 4, thereby enhancing assembling workability and enabling improving the heat conductivity from the longitudinal fins 9 and 15.

Embodiment 2

FIG. 8 is the schematic longitudinal sectional view showing a boiler according to Embodiment 2 of the present invention. The boiler according to Embodiment 2 is basically the same as the boiler 1 of the above Embodiment 1. In the following, a description will be centered on a difference therebetween, and corresponding portions are denoted by the same reference numerals.

The boiler 1 of the above Embodiment 1, the inner row communication portions 10 are provided to the lower end of the inner water tube row 7, and the outer row communication portions 16 are provided to the upper end of the outer water tube row 8. With this structure, the combustion gas from the burner 22 on an upper portion of the boiler body 2 flows through the inner row communication portions 10 at the lower end of the inner water tube row 7 into the combustion gas flow path 24 and is discharged to the boiler body cover 17 from the outer row communication portions 16 at the upper end of the outer water tube row 8. On the other hand, the boiler 1 according to Embodiment 2, the inner row communication portions 10 are provided to the upper end of the inner water tube row 7, and the outer row communication portions 16 are provided to the lower end of the outer water tube row 8. With this structure, the combustion gas from the burner 22 in the upper portion of the boiler body 2 flows from the inner row communication portions 10 at the upper end of the inner water tube row 7 into the combustion gas flow path 24 and is discharged from the outer row communication portions 16 at the lower end of the outer water tube row 8 to the boiler body cover 17.

In the case of Embodiment 2, at least the inner water tube row 7 is formed by alternately arranging the double-fin water tubes 11 and the no-fin water tubes 12 as in the case of the above Embodiment 1, or by successively arranging the single-fin water tubes 14 or the double-fin water tubes 11. When the boiler 1 is in the cold state, the distal end of the inner longitudinal fin 9 is close to the adjacent inner water tube 5. When the boiler 1 is in the combustion state, the gap between the adjacent inner water tubes 5 and 5 is closed. Other constructions are the same as those of the above Embodiment 1, so the description thereof will be omitted.

Embodiment 3

FIG. 9 is the schematic longitudinal sectional view showing a boiler according to Embodiment 3 of the present invention. The boiler according to Embodiment 3 is basically the same as the boiler 1 of the above Embodiment 1. In the following, a description will be centered on a difference therebetween, and corresponding portions are denoted by the same reference numerals.

In the above embodiments, the inner row communication portion 10 is provided to one end in the vertical direction (upper portion or lower portion) of the inner water tube row 7. In Embodiment 3 of the present invention, the inner row communication portion 10 is provided to a part in the peripheral direction of the inner water tube row 7. That is, in FIG. 9, in a predetermined region on a left peripheral side surface, the inner longitudinal fin 9 (and the inner water tube 5 in some cases) is not provided to the inner water tube row 7, and the inner longitudinal fins 9 are provided to the remaining portion over the entire area in the vertical direction of the gaps between the inner water tubes 5 and 5.

Further, in the above embodiments, the outer row communication portion 16 is provided to the other end in the vertical direction (lower portion or upper portion) of the outer water tube row 8. However, in Embodiment 3, the outer row communication portion 16 is provided to the other part in the peripheral direction of the outer water tube row 8. That is, as shown in FIG. 9, in a predetermined region on a right peripheral side surface, the outer longitudinal fin 15 (and the outer water tube 6 in some cases) is not provided to the outer water tube row 8, and the outer longitudinal fins 15 are provided to the remaining portion over the entire area in the vertical direction between the outer water tubes.

Also in Embodiment 3, a portion where the inner longitudinal fins 9 are provided is formed by alternately arranging the double-fin water tubes 11 and the no-fin water tubes 12 one by one as in the case of Embodiment 1, or by successively arranging the single-fin water tubes 14 or the double-fin water tubes 11. When the boiler 1 is in the cold state, the distal ends of each of the inner longitudinal fins 9 are close to the inner water tubes 5 adjacent to both sides thereof. When the boiler 1 is in the combustion state, the gaps with respect to the inner water tubes 5 adjacent to both sides are closed.

Further, in the case of Embodiment 3, a space between the outer water tube row 8 and the boiler body cover 17 on the outer side of the outer longitudinal fins 15 is closed by the fireproof material 20 and a heat insulation material or one of those. With this structure, the combustion gas from the combustion chamber 23 passes through the inner row communication portion 10 at the one end in the peripheral direction (left side in FIG. 9) and passes through the combustion gas flow path 24 between the inner water tube row 7 and the outer water tube row 8 to be discharged through the flue 19 at the other end in the peripheral direction (right side in FIG. 9). The flow path of the combustion gas is a laterally-oriented ω shape, so the boiler body is called a ω flow boiler body. Other constructions are the same as those of Embodiment 1, so the description thereof will be omitted.

The boiler 1 of the present invention is not limited to the above embodiments and can be modified. For example, in the above embodiments, while the inner water tube row 7 and the outer water tube row 8 are provided, the number of water tube rows can be increased or decreased as appropriate. Further, in the above embodiments, the lower portion of the boiler body 2 is closed and the burner 22 is provided to the upper portion of the boiler body 2. Conversely, there may be provided a structure in which the upper portion of the boiler body 2 is closed and the burner 22 is provided to the lower portion of the boiler body 2.

Further, in the above embodiments, the description is made of the example in which the boiler of the present invention is applied to a steam boiler. However, the boiler of the present invention may be applied to a hot water boiler or a heat medium boiler. Further, in the embodiments, instead of providing the burner 22, by providing a structure with which an exhaust gas is introduced into the inner side of the inner water tube row 7, the boiler of the present invention may be applied to a waste heat boiler or an exhaust gas boiler.

Further, in the above embodiments, the double-fin water tube 11 or the single-fin water tube 14 is obtained by welding the longitudinal fin (inner longitudinal fins 9 or outer longitudinal fins 15) to the water tube main body (inner water tube 5 or outer water tube 6), but the water tube main body and the longitudinal fin may be integrally formed. For example, by extrusion molding, the water tube main body and the longitudinal fin may be integrally formed.

Further, in the above embodiments, the double-fin water tube, 11 or the single-fin water tube 14 may be provided with the inner longitudinal fin 9 (or outer longitudinal fin 15) having a proximal end and a distal end each formed in advance in a circular arc shape so as to be fitted with the outer peripheral surface of the inner water tube 5 (or the outer water tube 6).

Further, in the above embodiments, heights, widths, and thicknesses of the longitudinal fins 5 and 6 are appropriately changed, and, as a matter of course, the numbers of water tubes 5 and 6 constituting the water tube rows 7 and 8, respectively, can also be appropriately changed. 

1. A boiler comprising: a plurality of heat transfer tubes arranged to form a cylindrical shape between an upper header and a lower header to constitute a heat transfer tube row; and a plurality of longitudinal fins provided to close gaps between the plurality of heat transfer tubes without connecting the adjacent heat transfer tubes, the plurality of longitudinal fins being provided to a portion other than one of one end in a vertical direction of the heat transfer tube row and a part in a peripheral direction thereof.
 2. A boiler according to claim 1, wherein: the heat transfer tube row comprises, in order to close gaps between each of the plurality of heat transfer tubes and the heat transfer tubes adjacent to both sides thereof, a plurality of double-fin heat transfer tubes each having the longitudinal fins on both sides thereof and a plurality of no-fin heat transfer tubes free from having the longitudinal fin; the plurality of double-fin heat transfer tubes and the plurality of no-fin heat transfer tubes are alternately arranged one by one; and the boiler further comprises a combustion chamber on an inner side of the heat transfer tube row, which communicates with a combustion gas flow path on an outer side of the heat transfer tube row through a portion free from having the longitudinal fin at the one end in the vertical direction of the heat transfer tube row.
 3. A boiler according to claim 1, wherein: the heat transfer tube row comprises, in order to close gaps between each of the plurality of heat transfer tubes and the heat transfer tube adjacent to one side thereof, a plurality of single-fin heat transfer tubes each having the longitudinal fin on one side thereof; and the boiler further comprises a combustion chamber on an inner side of the heat transfer tube row, which communicates with a combustion gas flow path on an outer side of the heat transfer tube row through a portion free from having the longitudinal fin at the one end in the vertical direction of the heat transfer tube row.
 4. A boiler according to any one of claims 1 to 3, wherein the plurality of longitudinal fins have a size achieving closure of gaps between the adjacent plurality of heat transfer tubes owing to thermal expansion by one of a combustion gas and an exhaust gas.
 5. A boiler comprising: a plurality of heat transfer tubes arranged adjacent to each other; and a longitudinal fin provided between the adjacent heat transfer tubes, wherein: one end of the longitudinal fin is fixed to one of the adjacent heat transfer tubes; and another end of the longitudinal fin abuts on another of the adjacent heat transfer tubes owing to thermal expansion by combustion of a fuel in a combustion chamber. 